a. Field of the Invention
The present invention relates to a system and method for assessing interference to a signal caused by a magnetic field. More particularly, in an exemplary embodiment, the present invention relates to a system and method for assessing interference to a positioning signal generated by a magnetic field-based medical positioning system caused by a magnetic field within which the medical positioning system operates.
b. Background Art
Systems and methods for determining and/or monitoring the positioning (i.e., position and orientation) of medical devices within the anatomy of a patient using magnetic fields are generally known in the art. A description of one such system can be seen by reference to U.S. Pat. No. 7,386,339 entitled “Medical Imaging and Navigation System” to Strommer et al., the disclosure of which is incorporated herein by reference in its entirety. Strommer et al. disclose a magnetic field-based medical positioning system (MPS) for ascertaining the position and orientation of one or more MPS sensors. More particularly, the MPS is configured to acquire positioning (localization) data (i.e., the position and orientation) of one or more MPS sensors located on or within a medical device or tool. The position and orientation of an MPS sensor may be based on capturing and processing signals received from the MPS sensor while in the presence of a controlled AC magnetic field. Accordingly, the MPS sensor(s) may comprise one or more magnetic field detection coil(s).
Known MPS systems, such as that referenced above, may include a magnetic transmitter assembly (MTA) and a magnetic processing core for determining position and orientation readings. The MTA is configured to generate a magnetic field(s) in and around a certain area or region of a patient's body, such as, for example, the chest cavity, in a predefined three-dimensional space. Each MPS sensor is configured such that when disposed within the magnetic field(s), it senses or detects one or more characteristics of the magnetic field(s), and generates a signal corresponding to the detected characteristic(s). The signal generated by the sensor is provided to the magnetic processing core, which is responsive to the generated signals and is configured to calculate three-dimensional position and orientation readings for each MPS sensor. Thus, the MPS enables real-time tracking of one or more MPS sensors in three-dimensional space, and therefore, the real-time tracking of the corresponding medical device or tool with which the one or more MPS sensors are associated.
These magnetic field-based systems are not without their drawbacks, however. For example, because the medical device or tool with which the MPS sensor is associated operates in an environment with a magnetic field-based MPS, it inherently operates in a volume with a relatively strong magnetic field generated by the MPS. As such, the magnetic field generated by the MTA, for example, or a parasitic magnetic field, may cause interference with the signals transmitted by the MPS sensor(s) to the processing core of the MPS. This interference may cause distortions in the transmitted signals, thereby potentially compromising the fidelity of the transmitted signal and potentially rendering the position and orientation determinations using the distorted signals unacceptably inaccurate.
One attempt to combat this interference and its effects has been to protect the positioning signal. More particularly, one conventional method of protecting the signal generated by the MPS sensor is to twist the conductors or wires used to connect the MPS sensor with the processing core into a twisted-pair. This arrangement of the conductors has a cancellation effect on the interfering magnetic field, thereby preventing, or at least substantially reducing, the distortion to the positioning signal. One inherent limitation to this technique or methodology is that there are places between the MPS sensor and the processing core where it cannot be applied. For example, in connection areas, such as, for example, in the handle or proximal portion of the medical device or tool wherein two segments of conductors (e.g., two segments of twisted-pair conductors) are connected via a connector, the twisted-pair cannot be used. If this connection area is disposed within a magnetic field, and the magnetic field is strong enough, it will interfere with the positioning signal as it travels therethrough, thereby distorting the signal.
Accordingly, there is a need for a system that will minimize and/or eliminate one or more of the above-identified deficiencies.